There has been significant interest and research in the field of solid state photoelectric and biochemical vapor and particle detectors. In detecting various species in vapor and particle form, various relatively complex and high cost solutions have been developed, but are unsuitable for low cost, portable devices operating at room temperature.
A PIN diode is a semiconductor diode with a lightly doped intrinsic semiconductor region in a substrate between a p-type region and an n-type region. For particle detection, when radiation or charged particles of sufficient energy impact the intrinsic region, an electron-hole pair is created that generates current between the p-type and n-type regions. The p and n-type regions and the intrinsic region also have a measurable capacitance. The PIN diode can be used to detect photons as well as various types of charged particles including alpha particles and beta particles in a variety of sensors, such as radon sensors, radiation sensors, light sensors, and smoke detectors, among others.
One difficulty with using PIN diodes for sensors is the lack of sensitivity to detect indirectly ionizing neutrons because the impact of a neutron in the intrinsic region does not directly generate current as neutrons are electrically neutral. Additionally, the usefulness of a sensor is often proportional to the sensitivity of the PIN diode. It is therefore desirable to provide PIN diodes with enhanced levels of sensitivity, and with the ability to detect neutrons and to identify changes in vapor content in an environment, in addition to, or instead of, charged particles and photons.